It is well known that a plurality of layers comprising a hydrophilic organic colloid (generally gelatin) may be provided on a support such as cellulose triacetate, polyethylene terephthalate or paper. These layers have various functions, for instance as a underlayer, interlayer, light-sensitive layer, protective layer, etc. Each layer contains various organic or inorganic additives to fulfill its function.
Generally, a photographic material comprises many hydrophilic organic colloid layers as mentioned above. In the preparation thereof, it is required that the coating solutions for these layers be uniformly coated in the form of a thin film at a high speed without causing any troubles in coating such as comet, repellent spots, and unevenness in coating. Continuous multi-layer co-coating methods have been carried out in recent years.
Coating steps in the preparation of color photographic materials are often difficult to perform. In the preparation of the color photographic materials, difficultly water-soluble additives such as color couplers, ultraviolet ray absorbers, brightening agents, etc., are dissolved in a high-boiling organic solvent such as a phthalic ester or a phosphoric ester and a co-solvent such as ethyl acetate. The resulting solution is dispersed (so-called emulsification) in a solution of a hydrophilic organic colloid, particularly gelatin, in the presence of a surfactant. The resulting emulsified dispersion is contained in a hydrophilic organic colloid layer.
When a large amount of a surfactant is used as the emulsifying agent for the formation of the above-described emulsified dispersion, it is difficult to coat a subsequent hydrophilic organic colloid layer on the previously coated hydrophilic organic colloid layer. On the other hand, when the amount of the emulsifying agent is reduced, the emulsion particles agglomerate, and the photographic characteristics of the coated photographic material are unstable.
One of the coating steps which is particularly difficult is the curtain coating method wherein a coating is carried out by forcing a coating solution in the form of a thin film to collide with a support described in JP-B-49-24133 (the term "JP-B" as used herein means "examined Japanese Patent publication") and JP-B-49-35447.
The most important question in the curtain coating method is how to coat rapidly and stably a coating solution in the form of a film. Many attempts and improvements have been made. Most of them have been directed to improvements in the devices for use in the coating step. It has been found that completely satisfactory results can not be obtained by these improvements in the devices, and the results greatly depend on the physical properties of the coating solution.
Various anionic surfactants have been conventionally examined as coating aids for various coating solutions for photographic materials. Concrete examples of the anionic surfactants are disclosed in U.S. Pat. Nos. 2,240,476, 3,026,202, 3,068,101, 3,320,847, 3,415,649 and 4,916,054, West German Patent 1,942,665, JP-B-59-50969, JP-A-2-178649 and JP-A-2-178648 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
However, most of these anionic surfactants do not provide satisfactory wetting, repellent spot inhibition and curtain coatability (thin film formation) in high-speed coating systems, which qualities have been particularly demanded in recent years.